Composite wire structures are commonly used as transmission lines or cable for transmitting electricity to users. Examples of composite transmission wire constructions include, for instance, aluminum conductor composite core (ACCC) reinforced cable and aluminum conductor steel reinforced (ACSR) cable. ACSR cable typically includes an aluminum outer conducting layer surrounding a steel inner core. The transmission lines are designed to not only efficiently transmit electricity, but must also be strong and temperature resistant, especially when the transmission lines are strung on towers and stretched over long distances. In fact, one of the major drawbacks of using steel-based transmission lines is that the cables tend to develop unacceptable sag when operating at higher temperatures.
To improve the properties of transmission lines, attempts have been made to construct the core of the cable with high strength polymers. U.S. Pat. No. 7,179,522 to Hiel, et al., for instance, describes a composite core formed from a carbon fiber-reinforced epoxy inner core surrounded by a glass fiber-reinforced epoxy outer core. According to Hiel, et al., the use of at least two different fiber types (carbon and glass fibers) is preferred to achieve a combination of strength, stiffness, and flexibility. Difficulties have nevertheless been encountered with composite cores containing more than one fiber type. For instance, because glass and carbon fibers have a different coefficient of thermal expansion, heat applied to the fibers during formation can cause the glass fibers to expand at a different rate than the carbon fibers. Upon cooling, the contracting glass forces the carbon into a compression state and results in residual stresses in the core. A few attempts have been made to make a core from a single fiber type. U.S. Patent Publication No. 2005/0186410 to Bryant, et al., for instance, describes attempts that were made to embed carbon fibers into a thermoplastic resin to form a single fiber composite core. Unfortunately, these cores exhibited flaws and dry spots due to inadequate wetting of the fibers, which resulted in poor durability and strength. Further, the carbon was susceptible to a galvanic reaction with aluminum, which could lead to corrosion and failure of the cable. Another problem with such cores is that the thermoplastic resins could not operate at a high temperature. For these reasons, Bryant, et al. developed a single fiber core that contained S-2 glass fibers embedded with a thermoset epoxy matrix. While such cores eliminated the problems of a two-fiber system, they nevertheless lacked the desired level of strength. Further, the use of thermoset resins is problematic in many manufacturing processes, and such resins also lack good bonding characteristics for forming layers with other materials.
As such, a need currently exists for a single fiber-type composite core that is formed from a thermoplastic material, and yet is still capable of achieving the desired strength, durability, and temperature performance demanded by a particular application.